Lennox SLP99UHV Series Unit Information page 65

E- Proper Gas Flow (Approximate)
TABLE 28
GAS METER CLOCKING CHART
Seconds for One Revolution
SLP99 Natural
Unit
1 cu ft
Dial
-070 55
-090 41
-110 33
-135 27
Natural-1000 btu/cu ft LP-2500 btu/cu ft
Furnace should operate at least 5 minutes before check-
ing gas flow. Determine time in seconds for two revolu-
tions of gas through the meter. (Two revolutions assures
a more accurate time.) Divide by two and compare to time
in TABLE 28. If manifold pressure matches TABLE 32 and
rate is incorrect, check gas orifices for proper size and
restriction.
NOTE - To obtain accurate reading, shut off all other gas
appliances connected to meter.
F-Check Manifold Pressure (FIGURE 50)
To correctly measure manifold pressure, the differential
pressure between the positive gas manifold and the neg-
ative burner box must be considered. Use pressure test
adapter kit (available as Lennox part 10L34) to assist in
measurement.
1 - Connect test gauge "+" connection to manifold pres
sure tap on the gas valve.
2 - Tee into the gas valve regulator vent hose and
connect test gauge "-" connection.
3 - Start unit on low heat (35% rate) and allow 5 minutes
for unit to reach steady state.
LP
2 cu ft 1 cu ft 2 cu ft
Dial Dial Dial
110 136
82 102
66 82
54 68
4 - While waiting for the unit to stabilize, notice the
flame. Flame should be stable and should not lift
from burner. Natural gas should burn blue.
5 - After allowing unit to run for 5 minutes, record
manifold pressure and compare to value given in
TABLE 32.
6 - Repeat steps 3, 4 and 5 on high fire.
7 - Shut unit off and remove manometer as soon as
an accurate reading has been obtained. Take care
272
to remove barbed fitting and replace threaded plug.
204
8 - Start unit and perform leak check. Seal leaks if
164
found.
136
G-Operating Pressure Signal (Delta P) Measurement
(FIGURE 51)
Operating pressure signal can be taken while the manifold
pressure pressure check is taken (using two measuring
devices). Or, taken after the manifold pressure measure-
ment is complete.
1 - Tee into the negative line between the gas valve and
pressure switch and connect to measuring device
negative "-".
2 - Tee into the positive line between the gas valve and
pressure switch and connect to measuring device
positive "+".
3 - Start unit on low heat (35% rate) and allow 5 minutes
for unit to reach steady state.
4 - After allowing unit to stabilize for 5 minutes, record
operating pressure signal and compare to value
given in TABLE 32.
5 - Repeat steps 3 on 4 high heat.
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